Stabilization of organic fluids against radiation decomposition and systems employing same



May 18, 1965 J. A. ELLARD 3,184,390

. STABILIZATION OF ORGANIC FLUIDS AGAINST RADIATION DECOMPOSITION AND SYSTEMS EMPLOYING SAME Filed Oct. 24, 1960 (R BOILER HEAT CON DENSER INVENTOR. JAMES A. ELLARD ATTORNEY United States Patent "Ice 3,184,390 STABlLlZATlON (BF ORGANIC FLUIDS AGAINST RADIATION DECOMPOSITION AND SYSTEMS EMPLUYING SAME James A. Ellard, Dayton, Ohio, assignor to Monsanto Company, a corporation of Delaware Filed (Bot. 24, 1960, Ser. No. 64,437 14 Claims. (Cl. 176-38) This invention deals with systems employing radiation stable fluids and particularly improvements in the art of cooling and moderating a neutronic reactor and the utilization of new compositions especially suitable for heat extraction from and moderating purposes within a neutronic power reactor.

It has been known for some time that the isotope U-235, occurring in natural uranium to the extent of one part in 139 parts of natural uranium could be fissioned by bombardment with thermal neutrons, resulting in the production of two lighter elements having great kinetic energy, together with approximately two fast neutrons on the average together with beta and gamma radiation. Vast amounts of heat energy are liberated in this reaction, and the recovery and use of such heat has presented attractive possibilities as a use of nuclear power.

The practical generation and recovery of the nuclear or atomic derived heat was, of course, dependent upon the successful solution of the problem of safely inducing and controlling a self-sustaining chain reaction. As is well known to those skilled in the art, this problem was solved by arranging bodies of the fissionable material, usually uranium or enriched uranium in a geometric pattern within a mass of moderator in such fashion that a self-sustaining controllable chain reaction was obtained. The considerable amounts of heat generated in the bodies of fissionable material were removed either by cooling these bodies with a gas or with a suitable liquid. As a re' sult there were developed two general types of neutronic reactors which came to be referred to as gas-cooled and liquid-cooled reactors.

For the purpose of recovering the heat liberated by the fissioned chain reaction and utilizing such heat in a heat engine of conventional type, the liquid-cooled reactor has received the greatest attention and it is with this type of reactor that this invention is concerned.

Methods for constructing and operating neutronic reactors for carrying out the chain reaction are well known in this art and are described, for example, by Fermi and Szilard in US. Patent No. 2,708,656, issued May 17, 1955. The descriptive matter of this patent is by reference incorporated herein and made a part of this disclosure. According to the disclosure of this patent, either light water, H 0, heavy water, D 0 or diphenyl (biphenyl) may be used as a moderator and coolant in the liquidcooled reactor.

Attractive possibilities are presented by the use of hiphenyl as a reactor coolant. The properties of this material, i.e., its relatively high boiling point at atmospheric pressure (255 (1.), its chemical composition consisting only of carbon and hydrogen, and its thermal stability make possible the operation of reactors cooled with this material at temperatures as high as 425 C., or higher for extended periods of time. A major drawback encountered in the use of this material lies in its relatively high freez- 3,184,390 Patented May 18, 1965 ing C.) or pour point, low boiling point (255 C.), and the fact that some polymerization takes place in the biphenyl as a result of radiolytic damage.

In copending application Serial No. 590,002, filed June 7, 1956, now US. Patent 2,902,425, low pour point reactor coolants and moderators are described which are monoisopropylbiphenyls or mixtures of monoisopropylbiphenyls with biphenyl employing not in excess of 20% by weight of biphenyl in the mixture.

Copending application Serial No. 727,999, filed April 11, 1958, now abandoned, describes reactor coolants and moderators which have advantages over both biphenyl and monoisopropylbiphenyl. These materials are lower alkylo-terphenyls and lower alkyl-m-terphenyls or mixtures thereof. Not more than about 50% by weight of lower alkyl-p-terphenyls can be tolerated in admixture with the other isomers and still have sufliciently low pour point.

The surprising discovery has now been made that bitumens are stabilizers for polyphenyls subjected to radiation such as alpha, beta, X- and gamma-rays, neutrons, etc. These bitumen stabilizers reduce radiolytic damage including gas and residue or polymer formation in polyphenyls even at high temperatures of the order of 300 C. and higher. The term polyphenyl is defined for the purposes of this application to include biphenyl, the terphenyls, allrylation products thereof wherein l or 2 and only minor amounts of 3 or more lower alkyl groups are added, and mixtures thereof. Bitumens include asphalt, tars, pitches, etc. For the purposes of this specification and claims bitumens are defined as carbon disulfide-soluble components of naturally occurring hydrocarbons, likewise residues obtained from the distillation of petroleum, likewise artificial hydrocarbon substances (e.g., tars and pitches). These bitumens will also contain small amounts of carbon disulfide-insoluble materials which are almost impossible to remove as a practical matter. This definition of bitumens which has been adopted for the purposes of this specification and the claims thereof conforms to the term as defined in the book, Asphalt and Allied Substances, Abraham, fifth edition, volume I, page 65, lines 1 and 2 (1945). Preferred bitumens are the high-boiling thermally refractory materials since, for example, for use in Coolants for neutronic reactors the coolants will be subjected to high temperatures. .At least a sufiicient amount to reduce the formation of residues from the polyphenyls but not more than an equal amount by weight based on the polyphenyl of the bitumens is used. Preferably the amount of bitumen used in mixture with polyphenyl is at least an amount sufiicient to reduce the radiolytic damage in polyphenyls by at least 15%, normally an amount in the range of about 3 to 50% by weight in the mixture with polyphenyl. Strictly as a matter of economics it would be preferred to use as large an amount of bitumens in the mixture with polyphe-nyl as possible, i.e., close to 50%. However other considerations will normally limit the amount of bitumens in the mixture for optimum mixtures to the range of about 5 to 25 Depending on the source and type of asphalt, it can be desirable to extract the asphalt with benzene or similar solvent to obtain the preferred bitumens substance, while in other cases the asphalt can be used as is as a bitumens stabilizer. A similar benzene extraction treatment can be desirable for certain types of coal tars and other bitumens sources; however, normally it will be convenient to use 1% the coal tar as is; Petroleum residuums will normally be used as is.

When the compositions of the invention are subjected to radiation, decomposition products are formed including gases and high boiling polymer or residual products sometimes called high boilers. In a neutronic reactor using the" compositions of the invention as moderators and/or coolants these high boilers steadily build up in the fluid, and they can be tolerated up to about 30% in the fluid Without a substantial decrease in heat transfer. It is pre ferred at least for nuclear reactor moderator and/ or coolant use that the percentage of high boilers in the fluid not exceed about 50%, more preferably about 40%.

It is an object of this invention to provide new and useful reactor moderators and/or coolants stabilised against residue formation due to radiation.

It is another object of this invention to provide a radiation-stable coolant usable in a system wherein radiation is present.

It is another object of this invention to provide a radiation-stable hydraulic fluid usable in a system wherein radiation is present.

It is'another object of this invention to provide new low cost neutronic reactor moderators and/or coolants.

It is another object of this invention to provide new compositions of matter having improved stability against residue formation when used as neutronic reactor moderators and/ or coolants.

It is another object of the invention to provide new compositions stabilized against radiation decomposition resulting in the formation of residue products.

These and other objects of the invention will become apparent as the detailed description of the invention proceeds.

An illustrative but non-limiting listing of polyphenyls stabilized by bitumens against residue formation from radi- V phenyl,- t-butyl-m-terphenyl, t-butyl-p-terphenyl, di-t-butylo-terphenyl, di-t-butyl-m-terphenyl, di-t-butyl-p-terphenyl, n-amyl-o-terphenyl, n-hexyl-m-terphenyl, etc. The location of the lower alkyl group or groups on polyphenyl rings can be on any of the available positions.

Of the compounds named specifically above biphenyl or the terphenyls are desirable in being the least expensive, and they are'usable in spite of their high pour points, although they tend to cause trouble in use with freezing up of linesparticularly during temporary shutdowns. Mixtures of the terphenyl isomers available commercially under the trademark Santowax R, are quite satisfactory. To obtain coolants and moderators having low pour point characteristics biphenyl, a terphenyl, or mixed terphenyl isomers are alkylated to preferably add one or two isopropyl or t-butyl groups.

j As nuetronic reactor moderators and/or coolants the wphenyls named in the two paragraphs immediately above can be used either singly or in admixture with other polyphenyls. The alkylated biphenyls and ter-phenyls can be made by methods which are illustrated in copending application Serial No. 727,999, filed April 11, 1958. To make methyl alkylated polyphenyl it is desirable in the used as is for reactor coolants and moderators with the added bitumens stabilizer, of course; however, it may be preferred to use distillation to separate out the desired monoand dialkyl portions. The alkylation process, of course, will result normally in a mixture of isomers wherein the alkyl groups are located in ortho-, metaand parapositions on the polyphenyl nucleus. The single isomer couldrbe used as neutronic reactor coolants and moderators, but actually it is preferred to use the mixed isomers.

To test the radiation stability of the compositions of the invention representative samples of'm-terphenyl and m-terphenyl with bitumens therein were irradiated with high energy electrons using a Van de Graaif generator as the source of radiation. I

A typical control experiment is illustrated as follows: 5 g. of m-terphenyl was charged to a stainless steel reactor provided with suitable inlet and outlet ports and a thin titanium window to admit the radiation. After the sample was added to the reactor, the reactor was flushed with nitrogen and then connected to a gas collecting bottle. The material was irradiated with the Van de Graaff electron source at 2 million electron volts (m.e.v.) and 250 microamperes (pa), for a total irradiation time of 200 minutes. The reactor was maintained at a temperature of 400 C., the thermocouple being placed in the coolest portion of the liquid. The radiation power input to the irradiated sample during the test was 20 watt-hours per gram of sample. Actually a number of different samples were irradiated simultaneously in separate reactors and in each run one or more of-these samples was a control sample. The individual reactors were mounted in openings in a metal block which was electrically strip heated to maintain the temperatures of the reactor at 400 C. (752 F.) a

To determine the net residue formation in the irradiated. samples distillations were made of representative aliquots of the samples before and after irradiation. Conditionsof distillation were adjusted so only the high boiling residues would remain in the distillation pot. 1 A cylindrical aluminum block having four cylindrical openings extend ing from one end to aboutthree quarters of the length of a block was the heating source of the distillation apparatus. A resistance heating jacket was wrapped around" a portion of the block not having the openings therein. The distillation flask was a test tube closed at the top having a side take-01f arm for the distillate removal. The block was, of course, positioned with openings up for use. The openings in the aluminum block was not much largerthan the outer diameter of the flask so the block heating surfaces fit quite closely around the flask. Slots were] cut length-wise along the sides of the aluminum blockbeginning at the end having the opening to accommodate the take-off arm of the flask and allowed the flask to be seated well down in the opening of the block; Vacuum distillation ofthe sample (about 1 gram) was carried out over a period of two hours at a pot temperature of about 200 C. and a head temperature of about 170 C. determined by measurement in the block at appropriate points and using 0.5 mm. of Hg pressure.

Residue determinations similar to the control run de-, scribed :above were made for the other control samples and the bitumens polyphenyl mixtures before and after irradiation. From this information weight percent blank, weight percent residue and percent residue reduction were calculated. The results of these experiments are reported in the following table:

*The temperatures of 315 C. and 400 0. associated with these two columns indicate the temperature at which the samples were irradiated.

The asphalt used as stabilizers for m-terphenyl data of which is reported in the table above were derived from different sources. Asphalt No. 1 was the benzene-soluble portion of a commercial roofing asphalt, asphalt No. 2 was the residuum from the vacuum distillation of East Texas crude, and asphalt No. 3 was the residuum from the vacuum distillation of Smackover crude. ination of the data in the table indicates that irradiation tests were made at two difiterent temperatures, namely, 315 C. and 400 C. It appears that the asphalt may be even more effective at the higher irradiation temperature. It must be quite obvious from the data of the table that asphalt is a very effective radiation stabilizer for m-terphenyl and that substantial savings will be accomplished by the use of asphalt as a radiation stabilizer for m-terphenyl especially at high temperatures. In a like manner other bitumens are to a degree radiation stabilizers for m-terphenyl and for other polyphenyls.

Use of petroleum residuum-terphenyl mixtures as a moderator and coolant in a power reactor The particular residuum to be used in this specific embodiment is the residuum derived by conventional commercial vacuum distillation of Smackover crude. The coolant mixture is residuum and 85% SantoWaX R. Suitably coal tars, asphalts and other bitumens can be used. A typical power reactor is illustrated diagrammatically in the flow sheet shown in the accompanying drawing.

In the drawing, numeral 10 indicates a cylindrical reactor shell constructed preferably to steel. Within the shell 10 is arranged a reactor core 11, which consists of plates of enriched uranium of such number, size, shape and composition as to be capable of becoming critical upon the addition of the organic moderator-coolant of the invention. Surrounding the cylindrical shell 1%} is a cylindrical reflector shell 12, which is also constructed of steel and which contains liquid reflector material, but a solid moderating material could be used. In the reac tor core are inserted the usual control systems, indicated by numerals 52 and 53, the construction of which and use thereof is described in the Fermi et a1. patent, referred to hereinabove.

Numeral 13 indicates a disengager or gas trap, which is merely a device for separating gas from liquid. The disengager is connected with the reactor shell 10 by pipe 14. The gas which is separated from the liquid coolant in 13 flows out by means of pipe 15, connected to pressure controller 16, which in turn is connected to condenser 17 by pipe line 18. Condenser 17 carries a discharge line or vent 19, permitting thedischarge of gases to the atmosphere.

Liquid coolant flows from disengager 13 through line 20 into pump 21 by means of which the coolant is circulated into and through heat exchanger or boiler 22 via line 23. Leaving heat exchanger 22 by pipe 24 the coolant, now reduced in temperature, is returned to reactor An exam- 6 shell 111 by line 24. Branch lines 25 carry the fluid into reflector shell 12 and thence by pipe 26 back into the main stream flowing into pipe 14.

Pipe line 27 carries a small stream of coolant from pipe 24 either into filter 28 via pipes 29 and 27 and pump 54, thence returning the flow of filtrate by pipe 30 to the main stream flowing in pipe 24, or by means of pipes 27, 31 and 32 into purification still 33. Heating coil in the reboiler section of still 33 provides the necessary heat for distillation, the liquid returning thence to pipe 24 by means of pipe 35.

Liquid coolant which is fed to still 33 flows through pipe 32 and enters the still first passing pressure reducing valve 36, by which means the flow is controlled to that required to keep the high boiling components at the desired level. Still 33 can operate at reduced or atmospheric pressure. The distillate in vapor form leaves the still by pipe 37 entering condenser 17, where the vapors are liquefied, the liquid resulting therefrom flowing through pipe 38 into pump 39 and being thereby returned by pipe 4% to the main stream flowing in pipe 20. Makeup liquid coolant is introduced into tank 4-1 and flows by pipe 42 into pipe 38 and thence into pump 39.

Purification still 33 may be operated continuously or intermittently as desired. It is, of course, desirable to keep the high boiling decomposition products in the circulating liquid as low as possible in view of the adverse elfects of these products on viscosity and heat transfer. Amounts of such high boiling decomposition products usually in the neighborhood of 540% by weight of the liquid can be tolerated without a substantial decrease in the heat transfer coefficient. After the high boiler content has reached a predetermined value (as determined by distillation of a sample), the purification still is placed in operation and a constant stream of coolant is withdrawn from the system into the still 33 where it is distilled. The distillate passes into condenser 17, where it is condensed and is then returned to the system by means of pump 39 as above described. The high boilers are removed from still 33 by means of pipe 45 containing valve 46 and are thcnceforth discarded.

Heat energy is withdrawn from the liquid coolant circulating in the heat exchanger or boiler 22 in any manner desired. In one method of operation, boiler feed water is introduced by means of pipe 5%? and steam is generated under pressure within boiler 22 withdrawn at pipe 51 and supplied to a steam turbine or other prime mover. The condensate produced in the conventional condenser forming part of the prime mover will again be returned to the boiler. It is, of course, not necessary that water be used, since a suitable thermally stable organic liquid may serve the same purpose and obviate the hazards encountered with accidental leakage of water into the coolant-moderator system. The further utilization of the energy obtained in this manner from a nuclear reactor is well known to those skilled in the art and forms no part of the present invention.

The system is filled with an inert gas such as nitrogen or helium, so as to eliminate traces of air and moisture pending the introduction of the coolant-moderator charge. The system is now loaded with the coolant-moderator by introduction to supply tank 41, from which point it is permitted to flow into and through the pipe lines and various pieces of equipment completely filling the same with the exception of still 33 and condenser 17 which are not filled. The system is filled to the point where the disengager is approximately one half full. Pump 21 is activated, the control devices in the reactor adjusted to release power in such an amount as to raise the temperature of the coolant-moderator in the system to a temperature in the range of about 300 to 450 C.,. preferably between about 350 and 425 0.; however, it'is possible higher temperatures will be desirable. Heat is extracted from the heat exchanger or boiler in the manner described above.

Radiolytic damage to the fluid is evidenced by the accumulation of fixed gases in disengager 13 and also by the formation of high boiling hydrocarbons in the liquid. The'fixed' gases consist of hydrogen and hydrocarbons. As the amount of fixed gas increases in the closed system, the pressure rises to the desired value, after which it is continuously or intermittently withdrawn through pressure control valve 16. Withdrawal of gas is controlled at such a rate so as to maintain the system under a pres sure which is sufliciently high as to minimize vapor formation in the hottest part of the system. This hottest part of the system is adjacent to the fuel elements in reactor 11. Decrease of density occurring as a result of increase in temperature will result in some loss of moderation by reason of the fewer hydrogen atoms per unit volume of coolant. Such decrease in moderation will, to some extent, damp out the nuclear reaction and can be compensated by adjustment of control devices.

The discharge of fixed gases attending the maintenance and the regulation of pressure upon the system will carry out some organic coolant-moderator in vapor form. In order to recover such coolant-moderator the gases are discharged into condenser 17, wherein they are cooled by contact with cooled surfaces maintained at a low temperature by means of cooling water. Condensed liquid organic coolant moderator will be returned by pipe to 38-, the valve therein now being opened intothe suction side of pipe 39 and thence returned to the circulating system.

The high boiling tar-like material formed concomitantly with thegases by the effect of radiation should also be removed or maintained at a desirably low level. This is done by the withdrawal via lines 27, 31 and 32 and reducing valve 36 of a constant stream of liquid flowing to' still 33. Still 33 operates under reduced or atmospheric pressure as a result of which the contents can be boiled by means of a side stream of fluid passing to heating coil 34, located within the reboiling zone of still 33. The distillate leaving the still passes by line 37 also into condenser 17. The. condensate is mixed with that derived from the disengager discharger vapors and'is then returned by pump 39 to the system.

Removal of solid particles from the interior walls of the system which become suspended in and are carried by the circulating liquid is best done by the provision of a filter 28located in the system asshown in the drawing. Such filter is supplied by lines 27 and 29 and the filtrate returned by line 30 to the system. The pressure drop across the filter may be overcome by means of a suit-able pump installed in either of these lines. By this means the induced radioactivity in the suspended foreign materials in the circulating fluid can be maintained at a low value.

Not only are the bitumens-polyphenyl mixtures usable as coolants and'moderators in neutronic reactors, but they are also'useful as coolants in any system employing radiation wherein the coolant must necessarily be subjected to radiation. For example, large food irradiators employing Co-60, Cs-137, spent fuel rods, or high intensity X-radiation or electron radiation using a fluid in hydraulic controls could very usefully employ bitumens stabilized polyphenyls as the hydraulic fluid.

Also, the bitumen radiation stabilizers of the invention can be used as radiation stabilizers for the poly(oxyphenylene)-benzenes, and particularly for these ethers of the wherein n is an; integer from about 3 to about 8, R is an alkyl radical having below about carbon atoms, i.e., methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl or mixtures thereof and x is an integer from 0 to 4 These stabilizers would be incorporated in the polyethers in less than equal amounts by weight based on the polyethers, preferably not more than about 10% by weight,

and suitably of the order of about 5% by weight. Although the invention has been described in terms of specified apparatus and materials which are set forth in considerable detail, it should be understood that this is by way of illustration only and the invention is not nec essarily limited thereto, since alternative embodiments and operating techniques will become apparent to those skilled in the art in view of the disclosure. Accordingly, modifications are contemplated which can be made without departing from the spirit of the described invention.

What is claimed is:

1.'A neutronie power reactor Wherein'the neutron mod- 7 erator comprises a mixture of non-fused ring polyphenyls and not more than 50% by weight of bitumens at least sufficient to inhibit the formation of residue from said polyphenyls, said bitumens being selected from the. class consisting of asphalt, coal tar, and petroleum residuum.

. 2.'A neutronic power reactor wherein the coolant for the fuel elements comprises a mixture of non-fused ring polyphenyls and not more than 50% by'weight of bitumens at least suflicient to inhibit the formation of residue from said polyphenyls, said bitumens being selected from the class consisting of asphalt, coal tar, and petroleum residuum. I

3. In a system employing radiation such as alpha, beta, X-rays, gamma-rays and neutrons and a coolant to regulate temperature in the system, said coolant being sub- ,jected to said radiation, the improvement wherein said coolant comprises a mixture of non-fused ring polyphenyls and not more than 50% by weight of bitumens at least sufiicient to inhibit the formation of residue from said polyphenyls, said bitumens being selected from the class consisting of asphalt, coal tar, and petroleum residuum. 4. In a system employing radiation such as alpha, beta, X-rays, gamma-rays and neutrons having a hydraulic system to operate the controls, the fluid for said hydraulic system being subjected to said radiation, the improvement wherein said fluid comprises a mixture of non-fused ring polyphenyl and not more than 50% by weight of bitu; mens at least suflicient to inhibit the formation of residue from said polyphenyls, said bitumens being selected from the class consisting of asphalt, coal tar, and petroleum residuum.

5. A composition stabilized against radiation such as alpha, beta, X -rays, gamma-rays and neutrons comprising a mixture of non-fused ring polyphenyls and from about 3 to 50% by weight based on said mixture of bitumens, said bitumens being selected from the class consisting of asphalt, coal tar, and petroleum residuum.

6. The composition of claim 5 wherein said polyphenyls are a mixture of terphenyl isomers and said bitumens are petroleum residuum.

7. A method of inhibiting theradiolytic damage to nonfused ringpolyphenyls under irradiation such as alpha, beta, X-rays, gamma-rays and neutrons at high temperature, which comprises adding to said polyphenyls a minor amount based on said polyphenyls of bitumens at least sufiicient to inhibit the formation of residue from said polyphenyls, said bitumens being selected from the class consisting of asphalt, coal tar, and petroleum residuum.

8. A method of claim 7 wherein said bitumens are added in an amount of about 5 to about 25% by weight.

9. A method of claim 7 wherein said bitumens are added in an amount of about 3 to 50% by weight.

10. A method of claim 9 wherein said polyphenyls are a mixture of terphenyl isomers and said bitumens are petroleum residuum.

11. A composition stabilized against radiationsuch as alpha, beta, X-rays, gamma-rays and neutrons comprising a mixture of non-fused ring polyphenyl isomers and from about 3 to 50% by weight based on said mixture of asphalt.

12. A composition stabilized against radiation such as alpha, beta, X-rays, gamma-rays and neutrons comprising a mixture of non-fused ring terphenyl isomers and from about 3 to 50% by weight based on said mixture of coal tar.

13. A method of inhibiting the radiolytic damage of a mixture of non-fused ring terphenyl isomers under irradiation such as alpha, beta, X-rays, gamma-rays and neutrons at high temperature, which comprises adding to said mixture of terphenyl isomers a minor amount based on said mixture of tcrphenyl isomers of asphalt in an amount of about 3 to 50% by Weight to inhibit the formation of residue from said mixture of terphenyl isomers.

14. A method of inhibiting the radiolytic damage of a mixture of non-fused ring terphenyl isomers under irradiation such as alpha, beta, X-rays, gamma-rays and neutrons at high temperature, which comprises adding to said mixture of terphenyl isomers a minor amount based on said mixture of terphenyl isomers of coal tar in an amount of about 3 to 50% by weight to inhibit the formation of residue from said mixture of terphenyl isomers.

References Cited by the Examiner UNITED STATES PATENTS 1,945,543 2/34 Weber 25279 2,003,888 6/35 Jamieson 106-279 2,346,947 4/44 Schloanstine 106279 2,861,894 11/58 Franck 106--279 2,870,080 1/59 Illman et a1. 106-279 FOREIGN PATENTS 798,029 7/58 Great Britain. 831,369 3/60 Great Britain.

OTHER REFERENCES TID-7007 (Part 1); Compilation of Organic Moderator and Coolant Technology, Melting Points and Viscosities of Mixtures of Diphenyl With Its Pyrolysis Products, by W. K. Anderson, page 129, January 24, 1957.

CARL D. QUARFORTH, Primary Examiner.

ROGER L. CAMPBELL, LEON D. ROSDOL,

Examiners. 

7. A METHOD OF INHIBITING THE RADIOLYTIC DAMAGE TO NONFUSED RING POLYPHENYLS UNDER IRRADIATION SUCH AS ALPHA, BETA, X-RAYS, GAMMA-RAYS AND NEUTRONS AT HIGH TEMPERATURE, WHICH COMPRISES ADDING TO SAID POLYPHENYLS A MINOR AMOUNT BASED ON SAID POLYPHENYLS OF BITUMENS AT LEAST SUFFICIENT TO INHIBIT THE FORMATION OF RESIDUE FROM SAID POLYPHENYLS, SAID BITUMENS BEING SELECTED FROM THE CLASS CONSISTING OF ASPHALT, COAL TAR, AND PETROLEUM RESIDUUM. 